The primary objective of this research program is to develop a microprocessor-based instrumentation system which will permit calculation of cardiac stroke volume, and consequently, cardiac output from signals which can be measured noninvasively. The pneumocardiogram (PNCG) is a record of the pulsatile cardiac-induced flow of air in the trachea. We have developed a pneumotachograph which is sensitive enough and responds rapidly enough to faithfully transduce the cardiac-induced air flow. In animal studies, we have demonstrated a correlation between the volume of air moved in the trachea with each heart beat and cardiac stroke volume. We have shown, however, that alteration of physiologic state alters the correlation between the PNCG and stroke volume and that there is a variation in the correlation between animals. The immediate objective of our current research is to investigate the genesis of the penumocardiographic signal. We are developing a model to include the factors which alter the relationship between the PNCG and stroke volume. An algorithm will be derived from the model and incorporated in a microprocessor-based instrumentation system which will display cardiac stroke volume. After verification of the instrumentation system in animal studies, the system will be modified for human application.